This invention relates to transmission systems in downhole components, more specifically to transmission systems comprising capacitors. U.S. Pat. No. 6,670,880, which is herein incorporated by reference, discloses a downhole transmission system through a string of downhole components. A first transmission element is located in one end of each downhole component, which includes a first magnetically-conductive, electrically-insulating trough, and a first electrically conductive coil lying therein. A second data transmission element is located in the other end, with a similar arrangement comprising a second magnetically-conductive, electrically-insulating trough and a second electrically conductive coil. The transmission system further comprises an electrical conductor in electrical communication with and running between each first and second coil in the downhole component. The string of downhole components is cooperatively arranged such that the components are in magnetic communication with each other and transmit signals through induction. Each downhole component comprises electrical characteristics such as impedance, reactance, capacitance and inductance.
Downhole tool strings may comprise components of different lengths. Some components are tools and others may be pipes. Depending on the function of the components, the length may vary. Many of the electrical characteristics of the component are dependent on the physical dimensions of the electrical conductor connecting the transmission elements, such as length and diameter. Impedance reflections may create noise between two conductors of different impedances, which result in signal loss and attenuation.
U.S. Pat. No. 2,414,719 assigned to Cloud, discloses a conduit for transmitting both fluids and pulsating electrical energy. The conduit comprises a plurality of pipe sections joined at each end, an insulated conductor extending along the conduit, and magnetic coupling means at a joint between two of the pipes for transmitting the electrical energy across the joint. The conduit further comprises a condenser and in one aspect a coil in the magnetic coupling means. The condenser, coil, and insulated conductor produce a circuit which passes only a selected band of frequencies whereby extraneous noises will not be transmitted along the conductor. FIGS. 8 and 9 of the '719 patent show a box comprising a condenser attached to a terminal of a coil, while another terminal connects the condenser to armored cable. The armored cable is attached to the box by fasteners. In this specification the term capacitor and condenser are considered equivalent.
U.S. Pat. No. 6,587,054 discloses an electrical submersible pump cable having an integral capacitor. The electrical submersible pump cable has a primary conductor with an insulator surrounding the primary conductor. A coaxial conductive layer surrounds the insulator, wherein the insulator serves as a dielectric between the primary conductor and the coaxial conductive layer. The coaxial conductive layer and primary conductor enable the coupling of data information onto and off of the cable.
U.S. Pat. No. 3,753,294 discloses a method and an apparatus, wherein the distributed capacitance between a conductor and the outer metallic armor of a cable is measured to enable a determination of the instantaneous changes in position of a tool supported by an elastic cable in a borehole. The correction calculated from the capacitance measurement is used to correct cable length measurements derived from a measure wheel which engages and rotates with movement of the cable.
It should be noted that the term “magnetically-conducting, electrically-insulating material” will be referred to in the rest of the specification as MCEI material.